We will investigate the thermodynamics of interaction in two and three component systems together with the protein structure induced by these interactions. The major apoproteins from human serum high density and low density lipoproteins will be used: 1. AI-phospholipid-cholesterol, 2. AII-phospholipid-cholesterol, 3. AI-AII (varying molar ratios)-phosxholipid-cholesterol, 4. Apo B-phospholipid-cholesteryl ester. These protein-lipid complexes will also be used to investigate the role of naturally occurring lipids in the recognition of HDL and LDL by their respective cellular receptors. This work will be carried out in collaboration with Dr. John Gwynne, Department of Medicine, University of North Carolina, Chapel Hill.